The present invention relates to an image forming device applied to a copying machine, a facsimile, a printer and the like. Specifically, the invention relates to an image forming device for forming an image in a way that the travel of developer from a developer carrier to a backside electrode is controlled by a developer passing controller based on an image signal and developer is attached on an image receiving member located between the developer passing controller and the backside electrode.
Recently, there is a strong demand for a copying machine or a printer capable of handing a mass of documents including color documents, accompanied with the improvement in the performance of a personal computer and the progress of network technology. However, it is still under development and expected to realize an image forming device which is capable of outputting black and white or color documents with sufficient and high quality and has a high processing speed.
As one of such technologies, the image forming technology called as xe2x80x9ctoner jet (registered trademark)xe2x80x9d where toner flies onto the image receiving member such as recording paper or an intermediate image carrying belt under the effect of electric field is known.
Such image forming devices are disclosed in Japanese Examined Patent Publication No. 44-26333, U.S. Pat. No. 3,689,935 (corresponding to Japanese Examined Patent Publication No. 60-20747) and Japanese Patent National Publication No. 9-500842. As one of examples, a prior art shown in Japanese Patent Application No. 10-100780 is explained in detail with reference to FIG. 17.
In FIG. 17, a grounded toner carrier 131 holds charged toner and conveys it. A regulating blade 132 manages toner layers from a single to triple on the toner carrier 131 and also charges toner. A supplying roller 133 supplies toner to the toner carrier 131 and charges toner. A toner passing controller 134 has a toner passing hole 135 formed therein and a control electrode 136 around the hole. A voltage corresponding to an image signal is applied to the control electrode 136 from a control power source 137. Reference numeral 138 is a backside electrode and reference numeral 139 is a backside electrode power source. Reference numeral 140 denotes an image receiving member such as recording paper conveyed on the backside electrode 138.
In this structure, a uniform toner layer is formed on the toner carrier 131 with the regulating blade 132 by operating the supplying roller 133 and the toner carrier 131, and conveyed. Under this state, a voltage is applied to the backside electrode 138 and the image receiving member 140 is moved. Then, the control power source 137 such as a driver IC applies a voltage corresponding to an image signal to the control electrode 136 in synchronization with the movement of the image receiving member 140. Thereby, toner on the toner carrier 131 flies onto the image receiving member 140 while passing through the toner passing hole 135 corresponding to the image signal and attaches to it. Thus, a desired image is formed on the image receiving member 140.
Here, in order to form a fine image such as 600 dpi (600 dots per inch) on the entire surface of the image receiving member 140, the toner passing holes 135 have to be arranged in such a pitch on the toner passing controller 134. However, it is difficult to arrange them in a single row. As shown in FIG. 18, the toner passing holes 135 and the control electrodes 136 are arranged in a plurality of rows (eight rows in the shown example). The toner passing hole 135 and the control electrode 136 are shaped in a circle. Connecting electrodes connecting with the respective control electrodes 136 are extended to the moving direction of the toner carrier 131 and on both sides thereof to avoid mutual interference and connected to lead terminals of driver ICs outputting control voltage, respectively.
FIG. 17 shows an example that the image receiving member 140 is made of recording paper and others and an image is formed directly on this means. However, there are variations of thickness of recording paper, change of its characteristics with humidity variation and deformation occurs easily during conveyance. In case of a color printer, it is difficult to synchronize timing of forming an image for every color because of variation in conveyance of recording paper. This causes poor image quality. In order to avoid it, as shown in Japanese Patent Application No. 10-100780, it is preferable that an intermediate image holding belt is used as the image receiving member 140 and an image formed on this belt is transferred to recording paper collectively.
Referring to FIG. 19, an endless image holding belt 143 as the image receiving member 140 is made of a film in which conductive filler is dispersed in a resin with its resistance of 1010 xcexa9cm and is rolled up between a pair of rollers 144a and 144b. A pickup roller 145 supplies a piece of recording paper 146 from a paper feed tray. A timing roller 147 synchronizes position of an image with the supplied recording paper 146. A transfer roller 148 transfers a toner image formed on the image holding belt 143 to the recording paper 146, sandwiches the image holding belt 143 with the roller 144a, and presses the belt toward the roller 144a. At the same time, the transfer roller receives transfer voltage. A fixation device 149 fixes the toner image on the recording paper 146 by heating and pressing the recording paper 146 where a toner image has been transferred.
The above image forming device, however, has the following problems in case when the widths of the control electrode rows and the toner passing hole rows in the longitudinal direction, where the toner passing hole and the control electrode around it are installed, are equal to or less than the maximum printing width of the image receiving member in a direction perpendicular to the moving direction of the image receiving member.
First, an image density is decreased or irregularity of the image density is yielded in the area at the right and left ends of a formed image.
Next, when the toner passing controller is shifted in the direction perpendicular to the moving direction of the image receiving member, the area where the control electrode opposed to the image receiving member does not exist, namely, the area where an image cannot be formed is generated.
In addition, when the toner passing controller is not located in parallel to the orthogonal line perpendicular to the moving direction of the image receiving member, an image forming area W20 is limited to W20=W10 cos xcex8 where the angle between the orthogonal line and the control electrode row is xcex8 and the width of the control electrode row in the longitudinal direction is W10.
The first problem will be explained hereafter with reference to FIG. 16A and FIG. 16B. FIG. 16A and FIG. 16B are diagrams showing the vicinity of the end portion of the developer passing controller. FIG. 16A is a cross section of the vicinity of the end portion of the developer passing controller. FIG. 16B is an upper view of the vicinity of the end portion of the developer passing controller. In FIGS. 16A and 16B, reference numeral 1 is the developer carrier, 2 is the developer layer formed on the developer carrier 1 and 3 is the developer passing controller. Further, reference numerals 4a, 4b, and 4c are developer passing holes and 10a, 10b, and 10c are control electrodes installed around developer passing holes 4a, 4b, and 4c, respectively. The control electrode 10c is the control electrode at the outermost end of the control electrode rows. Further, an arrow in FIG. 16A shows the electric power lines formed between the control electrodes 10a-10c and the developer carrier 1 when the developer carrier 1 is grounded and a positive voltage is applied to the control electrodes 10a-10c. 
The reason why an image density decreases at the right and left ends of a formed image is explained with reference to FIGS. 16A and 16B. Namely, since the control electrode 10b is adjacent to the control electrodes 10a and 10c, the electric power lines between the control electrode row and the developer carrier 1 in the area A in FIG. 16A becomes dense. On the other hand, means generating the electric field does not exist at the right of the control electrode 10c located at the outermost end. Hence, the electric power lines in the area B in FIG. 16A is expanded, and its density becomes sparse. Namely, the electric field strength in the area B becomes small compared with the area A. Therefore, the amount of the developer peeled off from the developer carrier 1 by the control electrode 10c at the outermost end and is a little. An image density printed by the control electrode 10c is lower compared with that by the control electrode 10b. 
Further, when the toner passing controller is detachable from the image forming device, a predetermined clearance is needed between the toner passing controller and the image forming device in order to make it ease to detach them. Therefore, the above second and third problems become serious since it is difficult to keep the toner passing controller at a regular position. Further, in case of a color image forming device having a plurality of toner passing controller, each color is not superimposed to a regular position, namely, so called color blur is caused, if the above 2nd and 3rd problems are not solved.
Further, in the above-mentioned image forming device, the distance from the toner passing controller 134 to the toner carrier 131 or the backside electrode 138 is from several to hundreds of microns. Hence, electrical field is concentrated easily to a conductor or the convex portion of the toner passing hole 135 since the toner passing controller 134 includes the minute control electrode 136, a conductor, and the toner passing hole 135. Similarly, the electric field is also concentrated easily at the ends of the backside electrode 138 and the toner carrier 131. Therefore, when the voltage from many hundreds to several thousand volts is applied to the backside electrode 138 and the control electrode 136, the electric discharge phenomenon occurs among the toner passing controller 134, the toner carrier 131, and the backside electrode 138. Hence, there is a problem of destroying each means and disarranging a toner image formed on the image receiving member 140.
Further, in the conventional constitution, a conductor group is installed in a base layer of the toner passing controller 134 at regulated intervals. Hence, ruggedness is seen at arraying cycle of the conductor group at the surface of the toner passing controller 134 at the side of the toner carrier 131. In this constitution, when the toner carrier 131 is rotated for a long time while contacting the toner passing controller 134, a convex portion of the toner passing controller 134 is worn out. Hence, a conductor portion of the toner passing controller 134 is finally exposed. Accordingly, there is a problem that the electric discharge phenomenon easily occurs between the convex portion of the toner passing controller 134 and the toner carrier 131.
Further, when a maintaining member maintaining the distance between the toner carrier 131 and the toner passing controller 134 is installed, the toner carrier 131 contacts the maintaining member and rotates for a long time. In this case, there is a problem where a toner layer formed on the toner carrier 131 is disarranged by the maintaining member or the maintaining member is deformed. Accordingly, the distance between the toner carrier 131 and the toner passing controller 134 is changed. Hence, there is a problem that irregularity occurs in an image density.
In addition, as disclosed in Japanese Patent No. 2769389, toner, attached to the toner passing controller 134, is drawn and removed by using an airflow generating member to prevent toner clogging at the toner passing hole 135. In this case, not only toner, attached to the toner passing controller 134, however also the toner passing controller 134 itself is drawn to the side of the airflow generating member with airflow. There is also a problem where load of the vacuum drawing power is charged to only one part of the toner passing controller 134 when airflow is locally formed, and the toner passing controller 134 is deformed accordingly.
In view of the above-mentioned problems of the prior art, the object of the present invention is to provide an image forming device capable of forming an image properly formed to the right and left ends and without color blur for a color image.
Further, in view of the above-mentioned problems of the prior art, the object of the present invention is to provide an image forming device which can stabilize image quality.
An image forming device of the present invention comprises: a developer carrier for carrying a charged developer; a developer passing controller having a plurality of developer passing holes through which the developer passes, applying a voltage corresponding to an image signal to a plurality of control electrodes arranged to surround the surroundings of the developer passing holes to control the passing of developer; an image receiving member for receiving the developer passed through; and a backside electrode installed at the back side of the image receiving member, drawing the developer, wherein the width of a control electrode row in a longitudinal direction, where the control electrodes are arranged, is wider than the width of an image forming area in a direction perpendicular to a moving direction of the image receiving member, and both ends of the control electrode row in the longitudinal direction are arranged outside the width of the image forming area. Accordingly, it becomes a constitution to have excess control electrodes outside an image forming area.
Accordingly, the area where the electric power lines becomes sparse is located outside of an image forming area and the uniform electric field strength is formed within the image forming area. Therefore, a preferable quality image without irregularity of the image density between the center part and the right and left ends of a formed image is obtained, since developer is moved to the developer passing controller within a uniform electric field strength area.
Further, a voltage is applied to an outside part from the width of an image forming area of the control electrode row so as to obstruct the passing of developer through the developer passing hole during time when image formation is operated. Hence, this prevents the passing of developer from the developer passing hole, arranged outside of the width of an image forming area, to the side where the backside electrode is arranged.
Further, the developer passing hole is formed only in the portion arranged inside the maximum width of an image forming area of the control electrode row. Hence, this overcomes a problem completely where the developer is spilt to the backside electrode from the developer passing hole, arranged outside the maximum width of the image forming area.
Further, a correction member for correcting an address of the control electrode, where the image signal is supplied, based on the relative position of the developer passing controller to the image receiving member, is provided. Hence, the image forming area width formed on the image receiving member is adjusted to the regular width through correcting the address by the correction member in order to supply image signal to the control electrode in the part corresponding to the area of the image forming area width even if it is not arranged at a regular position since the developer passing controller has the control electrode row of which width is wider than the image forming area width.
Further, the correction member comprises: a detection member detecting the relative position of the developer passing controller to the image receiving member; a calculating member calculating correcting data based on the detection signal sent from the detection member; and a storage member for storing the correcting data obtained from the calculating member. Hence, a series of every correcting operation such as detection, calculation and storage is omitted since the relative position of the developer passing controller, detected by the detection member, is stored in the storage member as correcting data.
Further, the above correction is implemented by installing the detection member and the calculating member in the image forming device only when it is necessary, if the detection member and the calculating member, provided in the correction member, are detachable from the image forming device.
Further, the above-mentioned correction member is installed on the image forming device where a plurality of the developer carriers and the developer passing controller are installed. Hence, a high quality image without color blur is output since developer for each color is given to a correct image forming position by the correction member, even if the developer passing controller for each color is not arranged at a regular position.
Further, the developer passing controller is detachable from a main body of the image forming device and the correcting operation by the correction member is executed every time when the developer passing controller is installed in the main body of the image forming device. Hence, the change of the printing width and color blur etc. are suppressed by the correction member even if the developer passing controller is repeatedly detached from the main body of the image forming device. Therefore, the performance of maintenance is improved since a clearance between the developer passing controller and its installation position is sufficiently secured.
Further, another image forming device of the present invention comprises: a developer carrier for carrying a charged developer; a developer passing controller having a plurality of developer passing holes through which the developer passes, applying a voltage corresponding to an image signal to a plurality of control electrodes arranged to surround the surroundings of the developer passing holes, to control the passing of developer; a voltage supplying member for supplying a voltage corresponding to the image signal; an image receiving member for receiving the developer passed through; and a backside electrode, installed at the back side of the image receiving member, drawing the developer, wherein an external electrode, installed outside at both ends of the control electrode row in a longitudinal direction where the control electrodes are arranged in a direction perpendicular to a moving direction of the image receiving member, receives a desired voltage. Hence, the decrease of density and the irregularity of density in the right and left ends in an image forming area are restrained since the uniform electric field strength is formed in the entire width of the control electrode row as well as the control electrode arranged outside of the image forming area width. At the same time, manufacturing the developer passing controller becomes easy since the manufacturing area of ring like electrodes and the developer passing holes is decreased.
Further, the external electrode may be extended in parallel to a lead line connecting the control electrode with the voltage supplying member. A developer layer formed on the developer carrier approaches the lead line while it is transported to the position opposed to the developer passing hole. The electric field is formed between the lead line and the developer carrier since an image signal to the control electrode is applied to the lead line. The developer layer supplied to the position of the end of the developer passing hole row passes the same electric field as the center part of the developer passing hole row since the external electrode is extended in parallel to the lead line. Hence, the developer layer is transported to the developer passing hole row without omitting the developer layer at the end of the developer passing hole row while transporting it.
Further, when a voltage of the same polarity as that of developer is applied to the external electrode, the adhesion of the developer having the forward polarity on the external electrode and accumulation thereon are prevented since developer having the forward polarity on the developer carrier receives the electric repulsion power from the external electrode.
Further, by superimposing an alternating current voltage to the external electrode, the adhesion and accumulation of developer of not only the positive polarity however also the inverse polarity on the external electrode is prevented. At the same time, even when the developer is attached on the external electrode, the ac electric field formed between the developer carrier and the external electrode comes to act as an electric field where the developer on the external electrode is collected to the side where the developer carrier is arranged.
Further, a voltage applied to the control electrode, which obstructs the passing of developer, may be applied to the external electrode during time of the operation of the image formation. In this way the electric field strength formed between the developer passing controller and the developer carrier is uniformed across the width of the developer passing hole row in the longitudinal direction without newly installing a power source for the external electrode.
Further, yet another image forming device of the present invention comprises: a developer carrier for carrying a charged developer; a developer passing controller having a plurality of developer passing holes through which the developer passes, applying a voltage corresponding to an image signal to a plurality of control electrodes arranged to surround the surroundings of the developer passing holes to control the passing of developer; an image receiving member for receiving the developer passed through; and a backside electrode, installed at the back side of the image receiving member, drawing the developer, wherein a width of an electrode row, arranged in an area which is adjacent to the developer carrier in the developer passing controller, is narrower than a width of a developer layer held on the developer carrier, viewed from a direction perpendicular to the moving direction of the image receiving member, and both ends of the electrode row are arranged inside both ends of the developer layer.
Further, yet another image forming device of the present invention comprises: a developer carrier for carrying a charged developer; a developer passing controller having a plurality of developer passing holes through which the developer passes, applying a voltage corresponding to an image signal to a plurality of control electrodes arranged to surround the surroundings of the developer passing holes to control the passing of developer; a maintaining member contacting a developer layer on the developer carrier and the developer passing controller to maintain a distance from the developer layer on the developer carrier to the developer passing controller constantly; an image receiving member receiving the developer passed through; and a backside electrode, installed at the back side of the image receiving member, drawing the developer, wherein a width of an electrode row, arranged in an area which is adjacent to the developer carrier in the developer passing controller, is narrower than a width of the maintaining member, viewed from a direction perpendicular to the moving direction of the image receiving member, and both ends of the electrode row are arranged inside both ends of said maintaining member.
Further, the width of the image receiving member is wider than the width of the backside electrode, viewed from the direction perpendicular to the moving direction of the image receiving member, and both ends of the image receiving member are arranged outside both ends of the backside electrode.
Further, the width of the developer passing controller is wider than the width of the developer carrier or the width of the backside electrode, viewed from the direction perpendicular to the moving direction of the image receiving member, and both ends of the developer passing controller are arranged outside both ends of the developer carrier or both ends of the backside electrode.
Further, the width of the developer layer is narrower than the width of the maintaining member, viewed from the direction perpendicular to the moving direction of the image receiving member, and both ends of the developer layer are arranged inside both ends of the maintaining member.
Further, the width of the developer passing controller is wider than the width of the maintaining member, viewed from the direction perpendicular to the moving direction of the image receiving member, and both ends of the developer passing controller are arranged outside both ends of the maintaining member.
Further, the width of the developer carrier is wider than the width of the maintaining member, viewed from the direction perpendicular to the moving direction of the image receiving member, and both ends of the developer carrier are arranged outside both ends of the maintaining member.
Further, yet another image forming device of the present invention comprises: a developer carrier for carrying a charged developer; a developer passing controller having a plurality of developer passing holes through which the developer passes, applying a voltage corresponding to an image signal to a plurality of control electrodes arranged to surround the surroundings of the developer passing holes to control the passing of developer; an image receiving member for receiving the developer passed through; a backside electrode having an opening, installed at the back side of the image receiving member, drawing the developer with electromagnetic force; and an airflow generating member drawing the developer adhered to the developer passing controller with airflow, wherein a width of the opening is wider than a width of an electrode row located in a region which is adjacent to the developer carrier in the developer passing controller, viewed from a direction perpendicular to the moving direction of the image receiving member, and both ends of the opening are arranged outside both ends of the electrode row.
Further, yet another image forming device of the present invention comprises: a developer carrier for carrying a charged developer; a developer passing controller having a plurality of developer passing holes through which the developer passes, applying a voltage corresponding to an image signal to a plurality of control electrodes arranged to surround the surroundings of the developer passing holes to control the passing of developer; an image receiving member for receiving the developer passed through, the image receiving member having a second opening; a backside electrode having a first opening, installed at the back side of the image receiving member, drawing the developer with electromagnetic force; and an if airflow generating member drawing the developer adhered to the developer passing controller to the first opening through the second opening with airflow, wherein a width of the first opening is wider than a width of the second opening, viewed from a direction perpendicular to the moving direction of said image receiving member, and both ends of said first opening are arranged outside both ends of said second opening.
Further, it is desirable that the above-mentioned electrode row has the control electrode row where the control electrodes are arranged and the external electrode, arranged outside both ends of the control electrode row in the longitudinal direction, receiving a desired voltage. Further, it is desirable that an insulation layer is installed in the area where both ends of the backside electrode are located in the back on the surface of the image receiving member opposed to the developer passing controller. Further, it is desirable that the maintaining member is made of an insulating material.